A cryptographic communication network is a network constituted by a plurality of nodes being interconnected via a plurality of links. Each node is provided with the functionality of generating random numbers and sharing them with an opposite node connected via a link, and the functionality of performing cryptographic communication via the link using the random numbers as a cryptographic key (referred to as “link key” hereinafter). Some of the plurality of nodes each are provided with the functionality of generating random numbers different from the random numbers used as a link key and functionality of transmitting the generated random numbers to another node via a link.
An application used on the cryptographic communication network is provided with the functionality of performing cryptographic communication with another application using other random numbers as a cryptographic key (referred to as “application key” hereinafter), the numbers different from those constituting a link key.
The functionality of generating and sharing a cryptographic key between nodes is realized by, for example, a technique generally referred to as quantum cryptographic communication. In this communication, a node generates a link key and an application key, encrypts the application key with the link key and transmits the encrypted application key to another node. This technique is sometimes referred to as quantum key distribution (QKD).